Патент USA US2046061код для вставки
‘2,046,061 Patented June 30, - 1936 UNITED STATES PATENT OFFICE 2,046,061 COATED METAL Leo P. Curtin, Cranbury, and James M. Payne, Carteret, N. J., assignors to Curtin-Howe Cor poration, New York, N. Y., a corporation of New York No Drawing. Application January 10, 1935, Serial No. 1,258 17 Claims. This invention relates to coated metals; and it comprises an article of steel or iron carrying a thin black surface layer containing vanadium in combination with oxalic acid, said layer being hard, permanent, elastic enough to resist flex ‘ ing to a marked degree and serving as a bonding agent between the metal and subsequently ap plied paint, cohering to both; and it further comprises a method of coating ferrous metal and 10 preparing it for painting wherein the cleaned or pickled ferrous metal is exposed to the action of a solution containing tetravalent vanadium and oxalic acid and is thereafter washed and dried; all as more fully hereinafter set forth and as 15 claimed. In the metal ?nishing industry, it is now cus tomary prior to painting to apply some type of a protecting coating to the clean metal; this pre , (Cl. 148-65) oping at 10 per cent of the rate at which the bright metal alone would rust. The coating is therefore a rust retardant. We have found that coatings satisfactory as a protective agent for iron and steel and as a bond- 5 ing agent linking paint to iron or steel can be made with a solution containing vanadium oxa lates; and that these coatings exhibit a further advantage in that they offer a considerable re sistance to rupture by ?exing. Sheet metal so 10 coated can be bent at a very sharp angle with no tendency for the coating to crumble, even at the inner edge of the bend. The coating im proves the resistance of the sheet metal to sharp, heavy impact and is fairly resistant to high tem peratures, even up to 300° C. In contradistinc tion to the usual types of coating, this may be described as rust-proo?ng; it is not merely rust liminary coating serving as a basis for subsequent painting, varnishing and enameling. For the most part, it is difficult to secure completely pro retarding. tective coatings with ordinary types of paints and ?rmly cohering coating is formed and, after washing and drying, the underlying bright metal is wholly protected. The solution is made by dis varnishes applied directly to clean naked iron or steel. One type of preliminary coating often used is that produced by the action of solutions of By immersing clean pickled sheet metal in an 20 acidi?ed solution of a vanadium oxalate, a dark, solving vanadium tetroxid with the aid of oxalic phosphoric acid or of acid phosphates, on iron. It contains ferrous phosphate and often other phosphates as well. A solution containing a acid and the same chemicals are used in replen ishment. A slight amount of oxalic acid in excess is employed but it is not necessary to have free manganous phosphate is sometimes used. acid present in greater amount than suffices to prevent hydrolysis of the vanadium oxalate. A 30 pH ranging from 1 to 3 serves well. The coating bath should be rather hot, somewhere between 50° C. and 99° C. The time of treatment varies When 30 such a phosphate coating is washed and dried, it serves as a good basis for varnish, paint and lacquer. These coating materials cohere or bond better to the phosphated surface than they do to the naked metal. Besides phosphoric acid, other acids have been used as coating agents, the coat ings consisting of metallic salts of the respective acids used. A difficulty with most of these coatings of the prior art is that they do not resist ?exing well; if 40 coated sheet metal is bent at a sharp angle, there is a tendency to open flaws and crevices. Coat ings satisfactory in most other respects are apt to be de?cient in this; the coated metal often will not stand the manipulation necessary in making 45 up various things; automobile bodies, for exam ple. With a rupture in the coatings due to ?ex from 4 to 5 minutes to several hours. With 4 or 5 minutes treatment, the bath ordinarily gives ex tremely thin black coatings; but the thickness is su?icient for some purposes. 5 A- heavier type of coating is obtained with immersion for several hours. The color of the coating varies from a rich lustrous black to a dull black. It may be made decorative, in event no after-painting is used. With a rich lustrous black in the coating and a layer of transparent varnish, decorative effects are obtained. In making a typical coating bath in the present 0 coatings, while customarily called “rustproof”, invention, 166 parts of commercial vanadium tetroxid, V204, are dissolved in 10,000 parts of water with the aid of 260 parts of commercial oxalic acid. This bath contains the equivalent of 1.66 parts V204 to 100 parts of water, but higher are actually more in the nature of rust re and lower concentrations can be used. tardants. coatings can be produced with V204 concentra tions ranging from 0.3 to 4.0 per cent. A bath s0 prepared may be used inde?nitely long with oc casional replenishment of the contained vana 55 ing, there is the possibility of what is called “creeping corrosion”; rust appears under the double coatings and spreads inde?nitely. These In damp locations, with any frac ture or abrasion of the coating which exposes bright metal, rusting of the whole surface ulti 55 matelv occurs; the rust, however, perhaps devel Good 2 r ’ 2,046,961 dim and oxalic acid. The'vanadyl oxalate may be used in the corresponding amount. Commer ciaii vanadium pentoxid, V205, may be used in re plenishing the bath; it being reduced by oxalic acid to the vanadyl form. Additions of oxalic acid should be in the amounts required to keep the bath clear. Should a sludgeaof insoluble ferrous oxaiate or of insoluble ‘reduced vanadium compounds form it can be cleared up by cautious additions or? strong commercial hydrogen peroxid solution in the right amount; Ferrous oxalate is converted into ferric oxalate. Weak solutions give an undesirable dilution and it is not ad vantageous to add enough 'peroxid to cause sub 15 stantial oxidation in the bath itself. Bubbling air through the bath is sometimes expedient. An addition of V205 can sometimes be utilized in producing the limited amount ofoxidation wanted. The precise nature of the solute con 20 tained in the bathimade as described ante is not known and it changes after use in coating ferrous metal. Reduction‘ appears to take place; triva lent vanadium appearing. Ferrous oxalate is special purposesgdesirable to heat it. Heating may be up to a low red heat, of even by direct impingement of a ?ame. The color changes from black to dark blue. Undoubtedly, the oxalate radical breaks up. The bluish coating left after heating, however, has substantiaiiy the same de sirable physical and chemical properties, as well as the rust resistance, 'as an unheated similar coating. 1 The coating bath in the present invention is 10, acid, having a pH between 1 and 3. Alkaline baths do not give the same results; a vanadium containing, rust resisting coating’on ferrous met al. In an acid solutiomthe vanadium is present as a cation and a coating is formed containing 15 vanadium without production of iron hydroxids; without rusting the metal. 1 As stated, the presence of iron compounds in the vanadium coating bath is often advantageous. Conversely, it is found that small additions of 20 vanadium compounds improve the action of other oxalate coating baths. Iron is commercially coated by treatment with a solution of ferric also present. Ferrous oxalate although insoluble i,oxalate and a small addition of a vanadium com arpound to this bath improves the results; it gives a 25 in water and in oxalic acid solutions, has a rather substantial solubility in a solution of vanadium oxalates. In the use of the bath with iron and steel, ferrous oxalate can be formed and go into solution. The presence of this ferrous oxalate in 30 soiution is apparently desirable, up to concen trations of about, say, 0.5 per cent ferrous oxalate in the bath. In forming the coating the iron metal is at tacked and there is a production of ferrous 35 oxalate, some of which becomes part of the coat ing. Some goes into the bath. In the coating, there are trivalent and tetravalent vanadium; there are derivatives of vanadium trioxidf'VzOs. Vanadium'forms a number of different oxids and 40 they combine among themselves, so that it is possible that intermediate oxids between the trivalent and tetravalent are present, these'being in'combination, probably, with theioxalyl radical, although "vanadites of vanadium" or of ferrous 45 iron may be present. In some instances the coat ing appears to contain a basic oxalate which may be a vanadyl oxaiate corresponding to the for mula V204.VO C294. As stated, the ‘path always contains more or 50 less iron and this iron is useful in forming and contributing the coatings. It has been found that good ' coatings may be ‘obtained with baths in which the amount of iron present is greater than that incident to the formation and solution 55 of ferrous oxalate. Small additions of ferrous oxalate are sometimes useful in bringing the bath to its steady state. Sometimes ferric oxalate is ' added. Good coatings can be made with a bath containing about equal proportions of vanadyl 80 oxalate and ferric oxalate; say about 1.5 per cent or‘ each. ' The composition of the coating layer in all cases is complex but whatever its composition, it has the describedadvantageous properties. Its 65 resistance to rusting is about fouftimes as great as that of similar commercial “rustproofed” metal produced by prior processes. In comparative tests of the prior material and the present mate rial, with plates or “panels” each carrying three 70 coats of lacquer, they were sharply scratched to expose bright metal and’ comparative observa tions made at weekly intervals showed about 4 fold resistance in the present material. As stated ante, the coating is resistant to heat; 75 and, as a matter of fact, it is sometimes, for better coating. .The coating is darker and its rust resisting properties are considerably improved. Iron can be coated in a solution of oxalic acid alone although its action isprather slow and an addition of a small amount of vanadium 30 oxalate improves the results. While we have particularly described the use of oxalic acid in making the bath, other organic acids may be used, but, as we at present think, Solutions made with citric and tartaric acids give coatings which, made ‘ with less advantage. under the conditions described, are not as good as those made with oxalic acid. Phosphoric acid used as a substitute for oxalic acid in the direc tions given ante, produces a coating better than is given by tartaric orcitric acid under the same conditions. Good coatings can be made by these other acids, but their properties are somewhat different from those of the coating made with oxalic acid. In all cases, the bath should be acid to the do; scribedtextent, with a pH between 1 and 3. re preserving the desired acidity an addition of acid sodium oxalate is useful as a buffer salt. What we claim is:- , 50 1. As a new manufacture, a ferrous metal ob ject having formed thereon a rustproo?ng co herent surface coating containing oxalates and vanadium. 2. The method of rustproo?ng ferrous metals which comprises immersing such metal in a‘ 55 slightly acid solution containing vanadium as an oxalate. . 3. The process of ‘claim 2 wherein the slightly acid solutionI has a pH between 1 and 3. 4. The process of claim 2 wherein.’ immer sion is at a temperature between 50°- and 99° C. 5. In the rustproo?ng of sheet metal, the process which comprises immersing a plurality of succes sive sheets in a replenished bath containing a 65 vanadium oxalate, replenishment being by addi tions of oxalic acid and V204 and the tendency of both to deposit insoiuble products being cor rected by occasional oxidative treatments. 6. In the process of claim 5, as an oxidative 70 treatment, bubbling air through the ‘solution. '7. In the precess of claim 5, as an oxidative treatment, an occasional introduction of V205. 8.-In the process of claim 5, introducing hy drogen peroxid as an oxidative treatment. 75 , 2,046,061 3 9. In rustproo?ng ferrous metal articles and providing a protective coating, the process which coherent surface coating of a vanadium com comprises immersing such an article in a re pound, said coating being impervious and being plenished bath containing vanadium and iron as oxalates with enough excess oxalic acid to keep the solution clear, withdrawing, washing and resistant to rupture by ?exing or impact. 14. The article of claim 13 wherein the coat ing containing vanadium has the characteristics of a baked vanadyl oxalate coating. 15. An article having a surface of ferrous metal having formed thereon a. protective coherent drying. 10. In the process of claim 9, the method of replenishment which comprises occasional addi 10 tions of V204, of oxalic acid in the amount nec essary to keep the solution slightly acid and of an iron oxalate. 11. As a rustproo?ng method for ferrous metal, the process which comprises forming upon a fer 15 rous metal article a coherent surface coating con taining oxalates and vanadium and afterwards heating the article to break up the oxalyl radical. 12. The process of providing ferrous metal ob jects with a rustproo?ng coating whichmomprises 20 immersing such an object in a slightly acid solu tion of a vanadium salt, the acidity having a pH value of ,1 to 3. 13. As a new manufacture, a ferrous metal ob ject having formed thereon a thin, black, hard, oxalate coating containing a substantial amount 10 of vanadium in addition to other metallic oxalates. _ 16. An article having a surface of ferrous metal having formed thereon a coherent protective coating containing a vanadium oxalate in addi tion to iron oxalate. 17. A process of providing ferrous metal ob jects with a rustproo?ng coating which com prises exposing such an object to the action of an acidulated solution containing a vanadyl salt of an acid of the group consisting of oxalic, citric, 20 tartaric and phosphoric acid. LEO P. CURTIN. JAIWES M. PAYNE.